I usually find that a slightly compressed load of stick powder works best for high velocity AND accuracy. Per the Lee reloading manual, when you start to compress a strick powder the peak pressure will not increase and might actually decrease until it gets highly compressed. Depending on bullet weight, Benchmark through Varget burn rates have worked best for me. But I hardly ever use a bullet light enough for Benchmark to be the best powder. IMR 8208 XBR is usually the fastest powder I use, but H4895 or Varget usually gets better accuracy AND velocity for me.
Per the Lee manual, a loose powder load will shoot differently if the rifle is pointed up, level or down. While a loose powder load might be OK for target shooting, I try to avoid it for hunting loads when a shot in any attitude is possible. Also, I start in the MIDDLE of advertised powder loads and work up or down, depending if wanting a heavy or light load. I have sometimes found the highest pressures around 85% capacity and under, and this is especially true in ANY magnum case, even if it does not have "magnum" in the cartridge name, such as .22-250 Rem, .243 Win, .270 Win, etc.
Also, velocity is related to pressure. If you are running significantly above a speed listed in a load manual, then know that you are also running a higher pressure, most likely.
It's not safe to work up max loads above any load manual unless you have a chronograph. Primer flattening or loose primer pockets occur at vastly different pressure depending upon brass and primer hardnesses.
I once got flattened primers in a .22-250 when I was 3 grains ABOVE the minimum load listed in the Nosler manual (I was at 85% capacity), but increasing the load relieved the pressure and was able to go beyond Nosler max all the way up to Lee max without primer flattening. Personally, I never use a field load that isn't at least 90% of case capacity.
About the only time you are in danger of being overcharged on powder these days is if you are using an old load manual. Any cartridge that is used in old military rifles will have very light loads listed in a modern manual. Rifles such as the CZ 527 that are used by government agencies can stand 5.56mm NATO loads, which are higher than .223 Rem loads. This is why I find my loads that shoot best in my CZ 527 rifles are often at or above maximum .223 Rem specs.
So ask Remington if your rifle is rated for 5.56mm NATO ammo. If it is, then it probably likes hot loads.
